Windows Vista system files

Hi.
Here's my problem, someone borrowed me a Windows Vista evaluation copy, and i installed it just to check it out but made the mistake of install it in a partition that wasn't empty (although not the original XP OS partition), so when i uninstall it, i ended up with over 10GB of useless system files that won't go away, because of their system or whatever attribute. Is there a way to get raid of those files without formatting the partition (i really can't format it), like force them to be normal files?